The present invention relates to a method employing electromagnetic waves to measure the distance and velocity of objects.
Various methods for measuring distances employing electromagnetic waves (e.g., radar) are known. With FMCW radar, electromagnetic waves are continuously emitted from a source while their frequency is modulated with essentially a ramp shape between two values. In the known methods of this type, the waves are reflected by the object whose distance from the source is being measured and the reflected waves are received. The received waves are mixed with simultaneously emitted waves. During the change in frequency, i.e., during the ramp of the modulation signal, the propagation delay and, consequently, the distance of the object can be simply inferred from the intermediate frequency acquired as a result of the mixing.
If the reflecting object moves in relation to the source, the reflected signal experiences a Doppler shift. This phenomenon is exploited in a method described in International Application No. WO 92/11543 for measuring distance and velocity. In that method, the difference in frequency during one rise and during one drop in the frequency of the emitted waves is measured, the velocity is calculated from the difference in the variations in frequency, and the distance is calculated from the average value of the variations in frequency.
In one variation of this known method, the wave reflected by an object, or rather the intermediate-frequency derived from it, is evaluated.
Unfortunately, the previously known methods permit the distance or velocity of only one object to be measured at any given time. Therefore, there is a need for a method in which the distances and velocities of several objects within the range of a measuring device may be determined.